Apparatus for drying

ABSTRACT

A woven wire cloth for forming the surface of a drier drum and composed of warp and weft strands of 0.003- to 0.015-inch diameter and having a projected open area of 10 to 40 percent with the strands being made of a metal alloy having a mean coefficient of expansion of less than 2 X 10 6 inches/inch/* F. in a temperature range of 0* F. to 400* F.

Elite Inventor John Gordon Buchanan [50] Field 245/8;

Polnte Claire,Quebec, Canada 162/348-352, DIG. l; l39/425.5; 75/123 K; 844,331 34/lll.95,ll5,243 F;l48/3l Appl. No. Filed [56] References Cited UNITED STATES PATENTS [22] July 24, 1969 [4S] Patented Aug. I0, I97! ll 3 0O 4 1 m M 8 n u a m m m H &r I. .m m m mmmo m PGHG.W 317 3346 9999 w 1111 n l/ll. 7 003 m m 726 E 655 1 m 8311 445 J n 2223 P 6 5 l, 5 5 0 .m o N m a C m i a m C e u .m 6 Q 9 9m m fiw rnmwn ml 59 m M -GM HUN AnorneyAlan Swabey B A 'l: A rf APPARATUS WoR DRYING A STIR C woven wire cloth for fonmng the su ace of a drier drum and composed of warp and weft strands of 0.003- to 0.0l5-inch diameter and having a projected open area of 10 to 40 percent with the strands being made of a metal alloy hav- 10 Claims, 3 Drawing Figs.

245/8 34/lll,75/12 ing ,a mean coefficient of expansion of less than 2X10 [51] llnt. inches/inch! F. in atemperature range of0 F. to 400 F.

mun/1s PATENIEU Auslolsn 3598.346

INVEN TOR John G. BUCHANAN APPARATUS FOR DRYING BACKGROUND OF INVENTION 1. Field of Invention The present invention relates to a woven metal cloth. More specifically, the present invention relates to a woven metal cloth suitable for forming the surface of drum-type web driers wherein the web is forced against the surface of the drum by a positive gas pressure and is drawn against the surface of the drum by a negative gas pressure and wherein the gas is hot.

2. Description of Prior Art Recently, advances have been made in the drying art, particularly, the art of drying paper webs wherein high-velocity hot air is impinged onto the surface of a web supported on a perforate support surface and held thereagainst by a negative pressure applied through the support surface. A major problem encountered in the development of such driers was the formation on the surface of the perforate support. Standard bronze woven wire surfaces were attempted, but these surfaces were distorted by the heat and became inoperative when directly contacted by the hot air on those occasions when the paper broke, exposing the cloth to hot air. To overcome these problems, the weaving pattern of these bronze wire surfaces was redesigned and the wires were arranged at an angle to the axis of the drum. However, this did not over come the difficulty. Surfaces other than metallic wire cloth have been tried but without success. Nonwoven porous structures are generally too thick if they are to give adequate sheet support. This results in their pores being complicated and irregular in shape thereby causing difficulty with plugging of the pores by fine particles dislodged from the paper surface and carried inwardly towards the interior of the drum.

SUMMARY OF PRESENT INVENTION The present invention provides a woven wire cloth, adapted to form the perforate support surface for driers of the type described hereinabove and overcoming the problems of the previous arrangements.

Broadly, the present invention relates to a surface covering for a perforate drier drum, said woven wire cloth comprising warp strands of 0.003- to 0.005-inch diameter, weft strands of 0.003- to 0.0l5-inch diameter, the spacing of said warp and weft strands being in the range of 25 to 100 strands per lineal inch, said wire cloth having a projected open area of at least l percent, said warp and said weft strands both being formed from a metal alloy having a mean coefficient of expansion of less than 2X10 inches/inch/ F. in the temperature range between 0 F. and 400 F.

BRIEF DESCRIPTION OF DRAWINGS Further features, objects and advantages of the present invention will be evident from the following detailed description of a preferred embodiment taken in conjunction with the accompanying drawings in which:

FIG. 1 is an isometric view of a woven wire of a 2-1 semitwill woven cloth of the present invention;

FIG. 2 is a schematic sectional view illustrating a drier incorporating the woven wire cloth of FIG. I; and

FIG. 3 is an exploded view of a preferred embodiment of a drum cover fabricated in accordance with the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS As shown in FIG. I, the wire cloth of the present invention preferably is a semitwill weave composed of warp and weft strands l4 and [2 respectively. Each of these strands l2 and I4 has been crimped during weaving to permit the formation of a more uniform upper surface II on the cloth, i.e. to facilitate the formation of a monoplanar surfaced cloth. By a monoplanar surfaced cloth, it is meant a cloth having at least one surface thereof as defined by high points on the warp and weft strands lying in a plane when the cloth is stretched under tension between two points. To obtain the monoplanar surface til, it is sometimes necessary to grind off the high spots of the wire strands as indicated at 16. The amount of material ground off the high points will normally be less than one-third the diameter of the wire and in any event, will never exceed abut one-half of the diameter of the wire.

It has further been found that the wires must have a diameter in the range of 0.003 to 0.015 inch. Different mesh counts will be required for different papers depending upon the end use of the paper. This is presently the case with the forming wire of the Fourdrinier paper machine, where, for resultant fine papers such as writing paper, bond paper, etc., require find mesh wires ranging up to 2-1 per inch and even higher for very special papers. Coarser papers for use in paper bags, cardboard boxes, etc., where printing is not required, can be manufactured with coarser wires with mesh counts as low as 30 strands per inch.

Many different weaves could be used in the operation of this invention but 2-1 semitwill weave is the best. In semitwill weaving, the weft wire can be made to rise upward to the surface of the cloth thereby improving the sheet support and decreasing the mark left by the wire.

This is not readily achieved in plain weave, for example, because the short span between warp wires does not permit the weft to be bent upwards to the surface of the cloth. On the other hand, weaves such as 3 and l twill do not have sufficient numbers of interlocking points and the resultant cloth is too sleazy for good operation. Preferably, the wire cloths of the present invention will be a 2-l semitwill weave incorporating 60-90 warps and 4070 wefts per lineal inch.

The strands l2 and 14 of the woven wire cloth of the present invention must be made of a nonexpanding metal wire, preferably a wire with a mean coefficient of thermal expansion of at most 2 microinches (2X10') ineh/ F. in the temperature range of 0 F. to 400 F. Some alloys having characteristics suitable for wires or strands of the present invention are indicated in table I.

Some of the nickel may be replaced with up to 5 percent cobalt and still provide an alloy of the desired low mean coefficient of expansion in the temperature range of 0 F. to 400 F., yet retaining the physical properties necessary to permit weaving. A very suitable commercially available nickel-iron alloy which has a composition substantially equivalent to No. 2 in table 1 is sold under the trade name Invar.

To permit proper weaving, the wire strands of the above alloys are annealed at a temperature above about l,200 F. and generally over l,500 F., the temperature being selected to produce the required ductility, depending on the wire diameter, number of strands per inch, etc. of the cloth to be formed without unduly weakening the wire.

The drier rim 20 of the present invention includes a perforate shell 21 covered by a plurality of layers of wire cloth as indicated at 10, 22 and 24. The surface of the drum is formed from the wire cloth 10 made as above described. It can be seen that the innermost mesh 24 consists of relatively large diameter wires 26 and has a relatively open weave of say about 10 strands per inch, while the intermediate mesh 22 is formed of an intermediate diameter wire 28 and has a closer weave of say about 40 strands per inch and the other surface forming wire 10 is formed of relatively small diameter wires. The open areas of the cloth l0 and meshes 22 and 24 progressively increase to provide channels enlarging as they approach theperforate drum 21. The wires 26 and 28 of the mesh 22 and 24 normally will be of stainless steel or the like, provided the surfacing cloth 10 is formed of low mean coefficient of expansion materials described above. However, in some cases, it may be necessary to make at least the wire 28 of nonexpanding alloy, particularly if a large drum is to be made. Surprisingly, it has been found that, provided the surfacing cloth 10 is formed as described herein, no problem is encountered with expansion of the meshes 22 and 24 rendering the surface cloth 10 inoperative for the purpose intended on average-sized drums.

In operation, the drum 21 covered with a cover fabricated as above described of the layers 10, 22 and 24 is arranged within a drier hood schematically illustrated at 30 (FIG. 2). This drier hood directs hot air against the surface of a paper web 32 carried on the surface 11 of the cloth 10 on the drum 2l. At the same time air is withdrawn from the area of the drum 2] opposed to the hood 30 via the suction gland 34, whereby a positive gas pressure is created on one side of the web 32 and a negative pressure is exerted on the other side thereof. These two unbalanced pressures tend to force the web into intimate contact with the surface 11 of the cloth l and it has been found that the surface 11 of the cloth must be specifically constructed to prevent wire marks from being formed on the dry web, yet must be sufficiently porous to permit easy drainage of moisture driven from the web and have openings of a sufficient size and regular surface to minimize fines buildup and plugging of the wire cloth. It is very important that this wire cloth 10 be able to withstand the high temperatures encountered in the event of a web breakage when the wire 10 is directly contacted by the hot gases from the drier hood 30 and is raised quickly to relatively high temperatures.

The temperatures achieved by the wire cloth 10 when suddenly exposed to the hot surroundings of the drier is intermediate between the temperature of the hood and the shell of the drier which lies underneath it. It is believed that this is because the shell is massive and cannot quickly rise to the temperature of the hot air and continues for some considerable time to remain at the temperature of the moist paper which covered the drum during normal operation. This temperature is about l60 F. On the other hand, the hot air being used for drying may be at a temperature of 800 F. and the surrounding hood 30 will be close to this temperature. lt has been found by experiment that when the paper is accidentally or suddenly removed, the wire cloth 10 immediately increased in temperature to about 250 F. 275 F. and gradually increases thereafter to about 350 F. but the temperature did not increase to the temperature of the surrounding hood.

Therefore, a covering material with low thermal expansion in the range of 0 F. to 400 F. is effective in preventing buckling even though the wire cloth 10 is exposed to much higher temperatures than 400 F.

Modifications may be made without departing from the spirit of the invention as defined in the appended claims.

lclaim:

l. A woven wire cloth for forming the exposed surface of a perforate drier drum, said cloth being composed of warp and weft strands of 0.003- to 0.0l5-ineh diameter, with the spacing of said warp and weft strands being in the range of 25 to strands per inch, said cloth having a projected open area of 10 to 40 percent, said warp and weft strands both being formed from a metal alloy having a mean coefficient of expansion of less than ZX inches/inch/ F. in the temperature range of 0 F. to 400 F.

2. A wire cloth, as defined in claim 1, wherein said cloth is formed by a semitwill weave.

3. A wire cloth, as defined in claim 2, wherein the number of said warp strands is in the range of 60-90 strands/lineal inch and the number of said weft strands is in the range of 4070 strands/lineal inch.

4. A woven wire cloth, as defined in claim 3, wherein said metal alloy is a nickel-iron allpiy.

5. A woven wire cloth, as efined in claim 3, wherern said cloth has a monoplanar surface which is in part defined by flat surfaces formed by grinding off high points on said wire to remove up to less than one-half the diameter of said strands.

6. A woven wire cloth, as defined in claim 4, wherein said cloth has a monoplanar surface which is in part defined by flat surface formed by grinding off high points on said wire to remove up to less than one-half the diameter of said strands.

7. In a web drier, a perforate drum, an inner woven wire layer adjacent peripheral surface of said drum, an intermediate woven wire layer overlying said inner layer, and an outer woven wire layer overlying said intermediate layer, said inner layer having a larger diameter wire strands than said outer layer, and having a larger open area than said outer layer, and said intermediate layer being made of wire of a diameter intermediate the diameter said inner and outer layers and having an open area intermediate said inner and outer layers, said outer layer being composed of warp and weft strands of 0.003- to 0.0] 5-inch diameter, said warp and weft strands being spaced in the range of 25 to I00 strands per lineal inch, said woven wire of said outer layer having a projected open area in the range c. l0-4() percent, said warp and said weft strands of said outside layer both being formed of a metal alloy having a mean coefficient of expansion of less than 2X10 inches/inch/ F. in the temperature of 0 F. to 400 F.

8. in a drier, as defined in claim 7, wherein said woven wire of said outside layer is formed with a semitwill weave.

9. in a drier, as defined in claim 8, wherein the number of said warp strands is in the range of 60-90 strands/lineal inch and the number of said weft strands is in the range of 40-70 strands/lineal inch.

10 In a drier, as defined in claim 9, wherein said metal alloy is a nickel-iron alloy.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 598,346 D ed August 10, 1971 Inventofl John Gordon Buchanan It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Abstracts, line 5, the expression "2 x 10 is to read In column 1, line 50, the expression "2 x 10 is to read lines 58-59, "semitwill" is to read --semi-tWill-- line 69, "semitwill" is to read --semi-twill-- In column 2, line 14, "find" is to read --fine-- and "2-1" is to read --strands--;

line 20, "semitwill" (both occurrences) is to read --semi-twill--;

line 31, "semitwill" is to read --semi-twill--; line 36, the expression "microinches (2 x 10 is to read --micro-inches (2 x lO' In column 3, line 47, the expression "250 F. 275 F." is to read --25o-275F.--.

In column 4, line 10, the expression "2 x is to read line 13, semitwill" is to read --semi-twill--; line 44, the expression "2 x 10 is to read --2 x 10- line 47, "semitwill" is to read --semi-twi1l--.

Signed and sealed this 11th day of July 1972 (SEAL) Attes t:

ilDll U'H') M, RlZTCI-IYZR, JR. ROB'WT GOTPSCIHLK Attesting Officer Commissioner of Patents )RM PO-1050 [10-69) USCOMM-DC 60376-P6Q 9 U 5, GDVEQNMENT PRINTING OFFICE 195! 0-366331 

2. A wire cloth, as defined in claim 1, wherein said cloth is formed by a semitwill weave.
 3. A wire cloth, as defined in claim 2, wherein the number of said warp strands is in the range of 60-90 strands/lineal inch and the number of said weft strands is in the range of 40-70 strands/lineal inch.
 4. A woven wire cloth, as defined in claim 3, wherein said metal alloy is a nickel-iron alloy.
 5. A woven wire cloth, as defined in claim 3, wherein said cloth has a monoplanar surface which is in part defined by flat surfaces formed by grinding off high points on said wire to remove up to less than one-half the diameter of said strands.
 6. A woven wire cloth, as defined in claim 4, wherein said cloth has a monoplanar surface which is in part defined by flat surface formed by grinding off high points on said wire to remove up to less than one-half the diameter of said strands.
 7. In a web drier, a perforate drum, an inner woven wire layer adjacent peripheral surface of said drum, an intermediate woven wire layer overlying said inner layer, and an outer woven wire layer overlying said intermediate layer, said inner layer having a larger diameter wire strands than said outer layer, and having a larger open area than said outer layer, and said intermediate layer being made of wire of a diameter intermediate the diameter said inner and outer layers and having an open area intermediate said inner and outer layers, said outer layer being composed of warp and weft strands of 0.003- to 0.015-inch diameter, said warp and weft strands being spaced in the range of 25 to 100 strands per lineal inch, said woven wire of said outer layer having a projected open area in the range of 10-40 percent, said warp and said weft strands of said outside layer both being formed of a metal alloy having a mean coefficient of expansion of less than 2 X 10 6 inches/inch/* F. in the temperature of 0* F. to 400* F.
 8. In a drier, as defined in claim 7, wherein said woven wire of said outside layer is formed with a semitwill weave.
 9. In a drier, as defined in claim 8, wherein the number of said warp strands is in the range of 60-90 strands/lineal inch and the number of said weft strands is in the range of 40-70 strands/lineal inch. 10 In a drier, as defined in claim 9, wherein said metal alloy is a nickel-iron alloy. 